High-density electromyographic assessment of stretch reflex activity during drop jumps from varying drop heights |
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| Institution: | 1. Department of Biomechanics in Sports, Technical University Munich, Germany;2. Centre for Sensorimotor Performance, The University of Queensland, Australia;3. Human Movement Science, Bundeswehr University Munich, Germany;1. Sport Sciences – Performance and Technology, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark;2. Department of Occupational and Environmental Medicine, Danish Ramazzini Centre, Aalborg University Hospital, Aalborg, Denmark;1. Department of Orthopaedic Sports Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany;2. Department of Biomechanics in Sports, Technische Universität München, Munich, Germany;3. BG Center Murnau, Department of Trauma and Orthopaedic Surgery, Murnau, Germany;1. Department of Nutrition and Human Sciences, University of Nebraska- Lincoln, Lincoln, NE 68510, USA;2. College of Health Sciences, Kinesiology, University of Texas at El Paso, El Paso, TX 39968, USA;3. School of Kinesiology and Physical Therapy, Division of Kinesiology University of Central Florida, Orlando, FL 32816, USA;1. Faculty of Medicine, Akdeniz University, Antalya, Turkey;2. School of Medicine, Koç University, Istanbul, Turkey;3. Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom;4. Neurology Department, Faculty of Medicine, Akdeniz University, Antalya, Turkey;1. University of Belgrade, Faculty of Sport and Physical Education, The Research Centre, Blagoja Parovica 156, Belgrade, Serbia;2. University of Delaware, Department of Kinesiology and Applied Physiology & Biomechanics and Movement Science Graduate Program, Rust Arena, Rm. 143, 549 South College Avenue, Newark 19716, DE, USA;1. Faculty of Sport and Health Science, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan;2. Faculty of Kinesiology, The University of Calgary, 2500 University Drive, NW, Calgary, AB T2N 1N4, Canada |
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| Abstract: | This study investigated how drop heights and their associated drop jump performance relate to stretch reflex modulations. Eleven male subjects performed ten drop jumps from each of three individually predetermined drop heights. These were the drop height resulting in maximal performance (OPT), as well as 10 cm below (LOW) and above (HIGH) maximal performance. To quantify drop jump performance the reactive strength index, derived from force plate measures, was used. High-density surface EMG provided both stretch reflex response timing and size, as well as novel insight into the associated motor unit recruitment via muscle fiber conduction velocity estimations. These measures were examined in the vastus lateralis (VL), soleus (SOL) and gastrocnemius medialis (GM).Drop jump performance improved by 9% (p < 0.001) from LOW to OPT and decreased by 5% (p = 0.008) from OPT to HIGH. Despite decreasing performance, stretch reflex responses were largest at HIGH. Stretch reflex responses timing did not change; staying within the short (SOL, <60 ms) and medium (VL, GM; 60–85 ms) latency response time-frames. Motor unit recruitment appeared to change across drop heights only for VL, whereas activation intensity only changed for SOL. These results indicate that during drop jumps above OPT neuromuscular modifications result in VL no longer being maximally recruited. |
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| Keywords: | Stretch-shortening cycle conduction velocity Multi-channel EMG Reactive strength index Motor unit recruitment Muscle-tendon complex |
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